1. Field of the Invention
Embodiments of the present invention relate to a liquid crystal display (LCD) device, and more particularly, to a transmitting-reflective (transflective) type LCD device. Embodiments of the present invention are suitable for a wide scope of applications. In particular, embodiments of the present invention are suitable for implementing a single cell gap type LCD device.
2. Discussion of the Related Art
Generally, LCD devices are driven in accordance with optical anisotropy and polarizability properties of a liquid crystal material. Liquid crystal molecules have long and thin shapes and tend to align themselves in the same direction under the influence of an electric field. In this respect, the alignment direction of the liquid crystal molecules can be controlled by applying a suitable electric field to the liquid crystal material. An image is displayed by controlling the alignment direction of the liquid crystal molecules to change the optical anisotropy of the liquid crystal material and polarize light propagating through the liquid crystal material.
The LCD device includes an array substrate with thin film transistors (TFT) and pixel electrodes; a color filter array substrate with a color filter layer; and a liquid crystal layer between the two substrates. Recently, an active matrix (AM) type LCD device has gained great attention due to the high resolution and good picture quality. The AM type LCD device includes TFTs and pixel electrodes arranged in a matrix configuration.
The LCD device cannot emit the light in itself. Thus, it is necessary for the LCD device to use an additional light source such as a backlight unit. However, the amount of light viewed through the LCD device is about 7% of the total amount of light generated from the backlight unit. Thus, a high luminance LCD device requires a large amount of light and increases the power consumption of the backlight unit. A heavy battery is required to power the backlight unit. However, the operating time of the backlight unit is limited in battery mode.
In the bright surroundings, it is difficult to recognize the images displayed on the LCD device. Accordingly, a transflective type LCD device has been studied and developed actively, which can use both the ambient light and the light generated from the backlight. The transflective type LCD device includes unit pixel regions, wherein each of the unit pixels has a transmitting part and a reflective part.
In the reflective part of transflective type LCD device, the ambient light or the light generated from the backlight unit passes through the liquid crystal layer, and is then reflected and again passes through the liquid crystal layer, whereby the light passes through the liquid crystal layer twice. For the transmitting part of transflective type LCD device, the light passes through the liquid crystal layer once. Accordingly, if the same voltage is applied to the reflective and transmitting parts, no image is displayed. In this respect, it is necessary for the transflective type LCD device to provide a dual cell gap structure where the cell gap of transmitting part is different from the cell gap of reflective part. That is, the cell gap (CG2) of transmitting part is about twice as large as the cell gap (CG1) of reflective part by forming a passivation layer having different thicknesses in the transmitting and reflective parts.
In a vertical alignment (VA) mode transflective type LCD device to form a multi-domain by forming a slit pattern in a pixel or common electrode, a dual cell gap structure is realized with an overcoat layer formed on a reflective part of color filter array substrate.
Hereinafter, the related art VA mode transflective type LCD device will be explained with reference to FIG. 1.
FIG. 1 shows a cross-sectional view of the related art VA mode transflective type LCD device. As shown in FIG. 1, the related art VA mode transflective type LCD device includes a unit cell divided into a reflective part and a transmitting part, wherein a cell gap of reflective part is different from a cell gap of transmitting part, which is referred to as a dual cell gap structure.
That is, first and second substrates 10 and 30 are provided in opposite to each other, and a liquid crystal layer 50 is formed between the first and second substrates 10 and 30. Then, a backlight unit (not shown) is provided below the first substrate 10, wherein the backlight unit emits the light.
The first substrate 10 includes gate and data lines (not shown) crossing each other to define a pixel region; a thin film transistor (not shown) formed adjacent to a crossing portion of the gate and data lines; a passivation layer (not shown) formed on the thin film transistor; a reflective sheet 11 formed on the passivation layer of reflective part so as to reflect the ambient light (natural or artificial light); an insulation layer 12 formed on the entire surface of the first substrate 10 including the reflective sheet 11; a pixel electrode 13 of transparent material formed on the insulation layer 12 and connected with a drain electrode of thin film transistor.
The pixel electrode 13 is provided with slit patterns 13a to divide the unit pixel region into multi-domains. Then, the second substrate 30 includes an R/G/B color filter layer 32 to represent colors; a common electrode 34 formed on the R/G/B color filter layer 32; and an overcoat layer 36 formed on the common electrode 34 of reflective part.
In the reflective part, the ambient light passes through the liquid crystal layer 50 at the second substrate 30, and is then reflected on the reflective sheet 11, and again passes through the liquid crystal layer 50, whereby the light passes through the liquid crystal layer 50 twice. For the transmitting part, the light passes through the liquid crystal layer once. In this case, since the cell gap (g1) of reflective part is different from the cell gap (G2) of transmitting part, the voltage properties of transmitting and reflective parts become consistent with each other by controlling the thickness of overcoat layer 36 formed on the common electrode 34 of reflective part.
However, the related art VA mode transflective type LCD device has the following disadvantages. First, it is necessary to perform the process of depositing the overcoat layer and patterning the overcoat layer to be left only on the reflective part. Also, the gap difference occurs between the transmitting part and the reflective part due to the overcoat layer when depositing an alignment layer on the entire surface of the substrate including the overcoat layer and performing the rubbing process, whereby the rubbing defective may occur.